The World’s Biggest Turbo Test!

After 5,000 miles and 50 dyno runs, we bring you…

Jason SandsSep 1, 2012
Turbochargers are perhaps the single most important component of today’s diesel engine, and perhaps the least understood as well. Why do we even upgrade our turbochargers? Is it for power, reliability, exhaust gas temperature (EGT) control, or all three? We set out to find the answer to these questions and more by performing one of the most comprehensive turbo tests ever.
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Since they’ve been around forever (and many of our readers are running them), we chose the line of Aurora turbochargers built by ATS Diesel Performance for our comparison. They range in inducer diameter from 57 mm to 71 mm, so we’d have a pretty broad range of compressors to choose from. During our testing, we’ve monitored peak horsepower, torque, boost, drive pressure, discharge temperature, peak EGT readings, cruising EGT readings, and spool rpm. We’ve also racked up thousands of miles of driving impressions on each to let everyone know just how they performed.
Photo 3/23   |   We did all our turbo testing at Advanced Product Engineering in Camarillo, California. Dyno operator Tom Habrzyk used a Superflow load dyno and multi-channel monitoring system to calculate drive pressure, boost pressure, and compressor discharge temperatures as well as horsepower and torque.
The Truck
The pickup we chose for this test is our ’95 Dodge Ram 2500, known as Project Triple Threat. With its 5.9L Cummins 12-valve engine making 433 rwhp at a toasty 1,600 degrees EGT on a stock Holset HX35 turbocharger, we felt this would be the perfect testbed for various-sized turbos. Going into this test, we didn’t know whether the turbos would increase power or not, as the engine already seemed to have enough air (the exhaust produced very little soot) with the HX35. As it turned out, we’d learn more than we could have imagined.
Aurora 3000 Turbo
The first turbo we tested was the 57mm-inducer Aurora 3000 offered by ATS. As it was advertised to support 350 to 450 hp, we surmised this turbocharger would be comparable to our stocker—only without the possibility of explosion. As it turned out, the Aurora 3000 actually spooled quicker than the stock version, especially during part-throttle conditions. It also made more boost, peaking at 49 psi (compared to 42 psi for the HX35). And although EGT still hit 1,550 degrees, that peak temperature came a lot later in the dyno run. The Aurora 3000 also made more power, peaking at 449 rwhp and 1,041 lb-ft of torque. There were no driveability issues (such as lag or surging), but our EGT level showed we were pushing the limits of the 3000’s horsepower range.
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Aurora 4000 Turbo
Our second turbo in the test was the billet-wheel Aurora 4000. With a 63mm inducer, it represented a mid-step in performance between large and small turbos. With the 4000 installed, one could tell the truck had a larger-than-stock turbo on it. It spooled later and would surge slightly on locked shifts into Overdrive at maximum boost. We also got some part-throttle surge with this turbo, probably due to the fact that we were at sea level with a tight exhaust housing. On the other hand, running the 4000 (which is rated for up to 625 rwhp) did have its benefits. Boost was up to 56 psi, while EGT dropped a whopping 200 degrees at wide-open throttle, to a mere 1,400 degrees. Remember, this was with no intake or intercooling modifications—just the turbo itself. Power was also up slightly, to 452 hp. What was surprising was that at 3,000 rpm, the Aurora 4000 was worth an additional 20 hp as compared to the Aurora 3000. This power increase came with no additional fuel and indicated a broader powerband that would translate into a faster truck. We ran the truck at the dragstrip with the 4000, and it made a 13.50-second pass (vs. 13.76 seconds with the stock turbo), which indicated it was indeed making more power.
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Aurora 5000 Turbo
ATS offers its Aurora 5000 turbo as its entry level large turbocharger. The 5000 is rated at 750 rwhp, and with its 71mm inducer, it’s no joke. The turbo is also based on a different frame (BorgWarner K31 versus BorgWarner S300), so we were interested to see how it would perform. When we rolled the truck onto the rollers with the 5000, we were surprised to see 464 rwhp, a good 12hp gain at the peak over the 4000 turbo. It also carried out power even further than the 4000 and made nearly 20 additional horsepower at the top of the powerband. ATS recommends a cam, headwork, and intercooler to make full use of this turbo, so we were surprised at how driveable it was with our stock engine.
Photo 6/23
Surging was minimal, especially considering it made a whopping 59 psi of boost at full tilt. Exhaust gas temperature dropped even further—to 1,350 degrees at wide-open conditions—but was a little toasty at part throttle. ATS doesn’t recommend this turbo for towing (we could hit 1,200 degrees uphill with our empty truck), but as long as you’re willing to drop down a gear and keep engine speed at 2,500 to 3,000 rpm, we could still see using it. It’s definitely a large turbo, but it’s one we could see living with every day—if we had a 600 to 700hp truck and wanted a single turbo.
Aurora Compound Turbos
The idea behind using two ATS Aurora turbochargers in compound is simple: You get the spooling ability of the 57mm Aurora 3000 turbo, with the airflow capability of the 71mm Aurora 5000 charger. Each turbocharger does half the work, which makes everything a lot more efficient and the vehicle much more driveable.
Photo 7/23
When we first drove the truck with the Aurora compounds on it, it felt even better than in theory. No matter how hard we tried, we could only hit 1,200 degrees on the pyrometer, and that was with a puzzlingly low 56 psi of boost. Since our Aurora 3000 was wastegated, we figured it was what was limiting our overall boost pressures. Plugging off the wastegate resulted in 65 psi, but the truck really didn’t feel any faster. When we hit the dyno, our seat-of-the-pants theories evaporated, as we only put down 432 rwhp and 900 lb-ft of torque. While boost hit 65 psi, drive pressure hit a scary 99 psi, so we connected the wastegate back up, which resulted in 57 psi of boost with 72 psi of drive pressure. Then we tried removing the air filter. No gain. We checked for leaks, nothing. When we checked boost pressure between stages, we found the 71mm Aurora 5000 charger was producing 40 psi, while the smaller 3000 was barely spinning, at a pressure ratio of only 1.3:1.
Our working theory for the 30hp power drop was that the power required to spin a second turbocharger and maintain the same boost level took a bit more horsepower in the compound setup. As for why the compounds were able to keep EGT so low (on the dyno they were only 1,100 degrees) yet not make any more power, we have no solution; that’s a puzzler for us.
COMPARING COMPRESSORS: Peak Boost
As we went up in turbo size, so did our boost numbers. The 3000 especially showed signs of petering out as the engine approached our self-imposed, 3,000-rpm engine speed limit, while boost continued to climb on both the 4000 and 5000 turbochargers. Also, as boost went up, so did power. More air was getting into the engine, which was making it more efficient, so it’s no surprise the big 71mm Aurora 5000 made the most boost, and the highest peak power. With the 3000 and 5000 in the compound arrangement, boost did indeed go up, but again, for mildly unclear reasons, the compounds actually made less power.
Photo 11/23   |   After about 1,000 miles of driving on the Aurora 3000, we got Brown’s Diesel in Riverdale, California, to throw on the larger 63mm Aurora 4000 turbo.
1209dp 18+worlds Biggest Turbo Test+torque Graph
  |   If you want a torquey engine with a large powerband, then the Aurora 3000 is the way to go. It lit much earlier in the RPM range and easily outpaced the other turbos with a whopping 1,041 lb-ft of torque.
Spool RPM
The problem with larger turbos is they spool much later in the powerband. The stock 5.9L Cummins in our ’95 Dodge was designed to make peak power at 2,500 rpm, which didn’t mean much of a powerband for the larger turbos. Therefore, our injection pump was outfitted with 4,000-rpm governor springs from Garmon’s Diesel to allow much greater engine speed on the dyno. Since the engine still has stock valvesprings, we limited engine speed to 3,000 rpm.
Photo 12/23   |   Our Aurora 5000 kit included a feed line, clamps, hoses, and a new discharge tube to adapt the larger compressor side to the stock intercooler.
The Aurora 3000 was noticeably better than all the rest of the turbochargers at spooling, contributing to the high torque number. The 4000 and 5000 spooled at close to the same rate, and they both spooled much later. The compound turbos were actually in the middle of the bunch and were comparable to the Aurora 4000. The added pressure on the compressor wheel of the Aurora 3000 (from the 5000 spooling) made it spool slower than it did as a single turbo.
Peak EGT
People don’t always choose turbos for power, there’s also reliability to be concerned about. For those who like full-throttle passing, towing, drag racing, or sled pulling, peak exhaust gas temperature (EGT) numbers are a major concern. While safe EGT numbers vary from truck to truck depending on engine design, 1,600 degrees is considered OK for drag racing or sled pulling, 1,400 is acceptable for 30-second bursts, and 1,200 degrees is considered safe for towing. Not paying attention to excessive EGT can result in broken turbine wheels, cracked exhaust valves, or damaged pistons. In other words, the damage is very serious.
With our stock turbo, we saw EGT in the 1,600- degree range, and with the Aurora 3000, our EGT dropped only slightly, to 1,550 degrees. The 63mm Aurora 4000 resulted in a huge EGT reduction to 1,400 degrees—and remember that’s with the stock intercooler and intake piping! The Aurora 5000 dropped EGT even further to 1,350 degrees, while the compounds wouldn’t break 1,200 on the pyrometer —no matter how long we stayed in the throttle.
Cruise EGT
If you’re wondering why we would monitor cruise EGT, it’s because exhaust gas temperature at a steady state is a good indicator of fuel economy. Believe it or not, turbo sizing comes heavily into play when mileage is concerned, and smaller chargers usually do a lot better at cruising speeds. At 65 mph, we could see a clear difference in all the turbochargers, as the Aurora 3000 hit 700 degrees on the pyrometer, the 4000 hit 750, and the 5000 hit 800. While 50-degree jumps may not sound like much, at low-load conditions that translates to 0.5 to 1 mpg. So if you’re running a single, keep in mind that a larger turbo will also get slightly worse fuel economy. With the compounds, EGT was a mere 600 degrees, so fuel economy numbers should be very impressive.
1209dp 19+worlds Biggest Turbo Test+drive Pressure Graph
  |   Since We had some sea level surge issues with the Aurora 4000, we surged the turbo on purpose during our dyno testing to see what would happen. While rolling into the throttle achieved a drive pressure curve (blue) getting into it hard and early resulted in an irregular fluctuating curve (red). This type of surge can usually be tuned out of a truck by adjusting the fueling.
So Which Turbo Should You Buy?
That is the question, isn’t it? And after our extensive testing, we can honestly say nothing beats the Aurora 3000 and 5000 compound turbos for overall driveability and towing, even with the slight power loss. They spool quick, have massive power capabilities (once we crank up the fuel a bit more), and even showed the best cruising EGT of the bunch (best fuel economy). If price is a concern, then we’d say you’re probably an Aurora 3000 or 5000 customer.
Photo 15/23   |   Our truck looked mean with the ATS Aurora 3000 and Aurora 5000 compound kit installed, which included new hot pipes, cold pipes, both turbos, an air filter, and a 5-inch downpipe.
The 3000 spools quicker than stock, made more power than the stock Holest HX35, and (most importantly) won’t blow up at high boost levels. If you’re willing to live with a big turbo that can crank out 700 rwhp, you might as well step all the way up to the 71mm Aurora 5000 and pretend that below-2,000-rpm engine speed doesn’t exist. But once the big turbo lights, hang on!
We would suggest the Aurora 4000 to larger-displacement guys, those folks with 7.3L Power Strokes, 6.7L Cummins, or 6.6L Duramaxes. On those rigs, the 63mm turbo should spool comparably to the factory version. Since we plan on hitting 700 rwhp or more and wanted near-stock driveability, the compounds were a no-brainer for us. Look for us to up the fuel on our ’95 Dodge very soon to take full advantage of our extreme airflow, as we now have an extra 400 to 500 degrees on the EGT gauge to have some fun with.
Photo 16/23   |   Getting the twins on the truck did take a little bit of fabricating, as a ½-inch divided spacer from Source Automotive had to be used to clear the exhaust manifold, the oil drains had to be connected with a Y-fitting to the front of the block, the factory transmission heat exchanger had to be removed (warm weather only, otherwise it should be relocated), and an extra oil feed line had to be made. The compounds were the only turbos that required any fabrication; the rest were a direct bolt-in.
Quick Specs
Aurora 3000 57mm/64mm/12cm2, Supports: 450 hp
Aurora 4000 63mm/70mm/12cm2, Supports: 625 hp
Aurora 5000 71mm/70mm/12cm2, Supports: 750 hp
Aurora 3000/5000 compound turbos, Supports: 750 hp
Want to Tow? get compounds!
We fooled around a little bit with the two-person Kalispell camper from Carson Trailer, hitting nearly 100 mph during EGT testing for an upcoming trailer tow world record attempt. We also did heavily loaded runs on the dyno to see how the different turbos performed, and it was during these tests that the compounds really shined. The 57mm Aurora 3000 was the best of our single turbos, registering 211 hp at a sustained EGT of 1,200 degrees. Since the compounds made an unreal 393 rwhp at a mere 1,100 degrees EGT, we had to look at the dyno sheet twice to believe our eyes. If you plan on towing with nearly 400 rwhp, however, keep an eye on your engine coolant and oil temperature gauges, as towing with that type of power will overheat your average diesel.
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Sources

ATS Diesel
Arvada, CO 80002
866-490-5573
www.atsdiesel.com
Brown's Diesel
Riverdale, CA 93656
559-867-1111
www.brownsdiesel.com
Big Power Diesel
Palmdale, CA 93550
661-212-8292
www.bigpowerdiesel.com
Advanced Products Engineering
N/A, AK
951-897-0678
www.elfwest.com

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